This invention relates to a method of regenerating a powdery ion-exchange resin and a system for regenerating it.
As means for removing solid impurities from a liquid, there is a precoat filter. The precoat filter has a filter member which is made of a holder precoated with a powder such as cellulose, diatomaceous earth and asbestos (hereinbelow, termed "filter aid"). The filter aid layer with which the holder is precoated removes the solid impurities in the liquid.
Recently, a precoat filter which employs as its filter aid a powdery ion-exchange resin disclosed in Japanese Patent Publication No. 44903 (1972) has come into use in nuclear and thermal power stations, etc. An example in which this precoat filter was applied to a nuclear power station is described in Japanese Laying-open Patent Publication No. 101394 (1977). More specifically, a condensing and desalting filter precoated with the powdery ion-exchange resin is disposed in the piping of the water feed system of a boiling water reactor.
In case where the filter aid layer formed by the precoating has gotten clogged by passing the liquid to-be-treated through the precoat filter for a predetermined time, the backwash is performed to strip off the filter aid with which the holder has been precoated and the solid impurities which have been removed thereby, and the stripped filter aid is put to an abandonment disposal. This is not exceptional even in the precoat filter which employs the powdery ion-exchange resin as the filter aid. Each time the backwash is performed, the powdery ion-exchange resin becomes a waste. Especially in the application to the nuclear power station, the used powdery ion-exchange resin produced by the backwash must be disposed of as a radioactive waste. Since the backwash of the aforecited condensing filter precoated with the powdery ion-exchange resin is carried out at a rate of one time in about ten days, the used powdery ion-exchange resin being radioactive or the secondary waste appears in large quantities.
The technology of regenerating granular cation- and anion-exchange resins for use in a desalting equipment has been established. Examples thereof are described in Japanese Patent Publications No. 9001 (1966), No. 41110 (1978) and No. 29734 (1980). In any of these examples, a solution which has a specific gravity intermediate between the specific gravity of the granular cation-exchange resin and that of the granular anion-exchange resin is used to separate the respective ion-exchange resins, whereupon the granular cation-exchange resin is regenerated with sulfuric acid and the granular anion-exchange resin with sodium hydroxide. As the solution for the separation, Japanese Patent Publication No. 9001 (1966) employs a sucrose solution, and Japanese Patent Publications No. 41110 (1978) and No. 29734 (1980) employ sodium hydroxide. The regenerating methods described in these official gazettes are difficult of regenerating the powdery ion-exchange resin in which a powdery cation-exchange resin and a powdery anion-exchange resin are attracted to each other by their static charges to form floc.